The strong coupling condition \(\Gamma \gg 1\)  ensures exponential decay when the \(S R\)  -transitions occur into the large number of the final states of the reservoir with \(n \le \Gamma \) . Then the wave function destructive interference suppresses coherent oscillations.
In the weak coupling limit, resonance transitions between the initial state \(S\)  and the reservoir state \(n=0\)  govern the dynamic behavior.
It is worth to note to the point that the decay rate predicted by the Fermi Golden Rule approximation is \(2\Gamma \) . The reason for the error is obvious: this approximation is valid only if the amplitude is a slow (in comparison with the rapidly oscillating terms) function
of time, what is evidently not the case for the essential oscillating contributions of the recurrence cycles in the strong coupling case
[1]}. All the more the subsequent revivals of the initial state amplitude for the cycles \(k \ge 1\)  can not be reproduced within the Fermi Golden Rule approximation.
